Snow and ice on concrete pavements such as airport runways, roads, sidewalks, bridges and the like can lead to significant traffic and safety issues. Thus, various compositions have been proposed to deice such concrete pavements. Historically, alkali and alkaline earth chlorides like sodium chloride, potassium chloride and calcium chloride have been used. These compounds while effective and relatively inexpensive are; however, very corrosive with respect to metals like iron, copper, aluminum, and the like. In addition, such chlorides can be harmful to the environment. Thus, while these materials may be acceptable in some applications, chloride-bearing deicers are not suitable for concrete surfaces, particularly those used by aircraft. Glycol-based formulations, urea-containing formulations and methanol-containing formulations have also been suggested. These formulations, however, can be toxic, corrosive, and some are highly flammable.
To overcome these problems, it has been suggested to use sodium or potassium acetate or formate solutions. See, for example, U.S. Pat. No. 5,064,551 to Smith et al. and U.S. Pat. No. 5,350,533 to Hubred et al. Such acetates and formates tend to be more environmentally friendly and less corrosive to metal objects. These compositions; however, tend to cause cracking and deterioration on the surface of the concrete structure and within the concrete matrix.
A major cause of this concrete deterioration is due to the alkali-silica reaction (ASR). Stark, D., Morgan, B., Okamoto, P. and Diamond, S. “Eliminating or Minimizing Alkali-Silica Reactivity.” SHRP-C-343, Strategic Highway Research Program, National Research Council, Washington, D.C., 1993, 226p. ASR, in addition to cracking, can cause deleterious expansion and surface spalling. ASR is a condition that exists in concrete because of four main factors: reactive silica, which is supplied by the aggregates in the concrete; a high pH in the pore solution, high enough to begin to dissolve whatever species of reactive silica is present (different thresholds for different species); significant sodium and potassium ions to combine with the dissolved silica and form reactive gels (ASR reaction product); and, sufficient moisture to first enable the reactions to proceed at all (i.e., providing a medium for ion transport), and secondly, to supply moisture to the gels which will absorb it and expand.
ASR can weaken the ability of concrete to withstand other forms of attack. For example, concrete that is cracked due to this process can permit a greater degree of saturation and is therefore much more susceptible to damage as a result of “freeze-thaw” cycles. Similarly, cracks in the surfaces of steel reinforced concrete can compromise the ability of the concrete to keep out salts when subjected to deicers, thus allowing corrosion of the steel it was designed to protect. ASR can also cause the failure of concrete structures. Prior attempts to control ASR include, for example, using cement with very low alkali content, non-reactive aggregate, and pozzolanic materials such as fly ash, silica fume, ground blast granulated furnace slag, zeolite minerals, thermally activated clay, and the like.
Lithium-based compounds have been shown to be effective in ASR inhibition by introducing these chemicals into concrete or mortar mix compositions. W. J. McCoy and A. G. Caldwell, “New Approach to Inhibiting Alkali-Aggregate Expansion,” J. Amer. Concrete Institute, 22:693-706 (1951). However, this requires introducing the lithium-based compounds in the concrete or mortar mixture and does not address the problem of controlling or remediating ASR in existing hardened structures or the deicing issues.
Thus, a need has been identified for a composition that is an effective deicer and that significantly reduces deleterious ASR effects of sodium and potassium chloride or acetate compositions.